The present invention relates to a process for producing a rubber-based composite material including a substrate and a rubber joined to each other, and particularly to a process for producing a rubber-based composite material by forming an adhesion film on a substrate to be mated with a rubber for constituting the composite material, and laminating a rubber composition on the adhesion film and vulcanizing the rubber composition.
As a composite material including a rubber joined to a substrate such as a metal, a ceramic, a plastic, etc. which is used, for example, as a reinforcing member in tires, belts or the like, there are those in which a substrate and a rubber are joined to each other by vulcanizing and press bonding a rubber composition to the substrate. In these composite materials, not only the characteristics of the substrate and the rubber but also the adhesion between the substrate and the rubber affects greatly the characteristics of the composite material. Such rubber-based composite materials are required to show a high adhesive strength immediately after adhesion and after a long lapse of time.
As a process for producing a rubber-based composite material as above-mentioned, there are known, for example, methods of producing a rubber-plastic composite material in which a thin film of a metal or a metallic compound is formed on the surface of a plastic substrate, and a rubber composition is vulcanized and press bonded using the thin film as an adhesion film (see, for example, JP-A 62-189117 and JP-A 2002-172721).
In these methods, however, it is impossible to impart a strong adhesiveness to both the substrate and the rubber, and, therefore, the adhesive force has been insufficient between the substrate and the adhesion film and/or between the adhesion film and the rubber. In order to solve this problem, there has been proposed a method in which two adhesion films are used. In this case, on the contrary, good adhesion is required also between the two adhesion films. Accordingly, these rubber-based composite materials have been unsatisfactory as to initial adhesion performance, durability of adhesion, and storage stability.
In addition, the above-mentioned patent references report also the use of an alloy adhesion film, in which an alloy composed of the metal components is used as a target. In the case of such rubber-based composite materials, the metallic composition of the adhesion film or films should be varied according to the kinds of the substrate and the rubber. For this purpose, it is necessary to prepare a multiplicity of alloys differing in composition and to replace the target each time for providing the adhesion film with the desired composition. However, in order to replace the target, it is necessary to break the vacuum pressure each time. In this case, it is also necessary to prevent the outside air from being mixing into or remaining in the chamber at the time of replacing the target. Therefore, the target replacing operation would be extremely complicated and inefficient. Accordingly, it has been difficult to optimize the metallic composition of an adhesion film containing a plurality of metallic components according to the kinds of the substrate and the rubber.